Devira Larasati, et al. “Analysis of the Single Index Model and Markowitz in Optimal Portfolio Selection in the Telecommunications Sub-Sector Listed on the Indonesia Stock Exchange for the Period 2020-2022”. Finance : International Journal of Management Finance, vol. 1, no. 2, Dec. 2023, pp. 71-85, https://doi.org/10.62017/finance.v1i2.27.